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The table below s ummarizes the important features of the different kinds of RAID supported by the
Smart Array controllers. The decision chart in the following table can help determine which option is
best for different situations.
Table 12 Summar y of R AID met hods
RAID 0
Striping
(no fault
tolerance)
RAID 1+0
Mirroring
RAID 5
Distributed
Data
Guarding
RAID ADG
Maximum number of
hard drives
N/A N/A
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Storage system
dependent
Tolerant of single hard
drive failur
e?
No
Yes Yes Yes
Tolerant of multiple
simultaneous hard drive
failures?
No
If the failed
drives are not
mirrored to each
other
No
Yes(twodrivescanfail)
Online Spares
Further protection against data loss can be achieved by assigning an online spare (or hot spare) to any
configuration except RAID 0. This hard drive contains no data and is contained within the same storage
subsystem as the other drives in the array. When a hard drive in the array fails, the controller can then
automatically rebuild information that was originally on the failed drive onto the online spare. This quickly
restores the system to full RAID level fault tolerance protection. H owever, unless RAID Advanced Data
Guarding (ADG) is being used, which can support two drive failures in an array, in the unlikely event that
a third drive in the array should fail while data is being rewritten to the spare, the logical drive still fails.
Logical storage elements
Logical storage elements consist of those components that translate the physical storage elements to file
system
elements. The storage server uses the Window Disk Managem ent utility to mana ge the various
types o
f disks presented to the file system. There are two types of LU N presentation: basic disk and
dynamic disk. Each of these types of disk has special features that enable different types of management.
Logical drives (LUNs)
While an array is a physical grouping of hard d rives, a logical drive c onsists of components that translate
physical storage elements into file system elements.
It is important to note that a LUN may extend over (span) all physical drives within a storage controller
subsystem, but cannot span multiple storage controller subsystems.
L4
L5
L3
A1
L1
L2
A2
gl0045
Figure 20 Two arrays (A1, A2) and five logical drives (L1 through L5) spread over
five physical drives
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Storage management overview